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Identification of Rhizoctonia solani AG-UNK from Rice and Rice Fields in Texas as AG-11
1Department of Plant Pathology, University of Minnesota, St. Paul 55108.
Plant Disease
|March 8, 2019
Summary
Rhizoctonia solani AG-11, previously unidentified in Texas, was discovered in rice fields. This finding confirms the identity of previously unknown isolates and expands the known distribution of this fungal pathogen in the United States.
Area of Science:
- Plant Pathology
- Mycology
- Agricultural Science
Background:
- Survey of Texas rice fields in 1984-1985 identified Rhizoctonia solani AG-1 IA and R. oryzae.
- Eight multinucleate Rhizoctonia solani-like isolates were collected, initially characterized as R. solani AG-UNK (2) due to lack of anastomosis with existing testers (AG-1 to AG-8).
- These isolates were recovered from soil and stem lesions, exhibiting low frequencies compared to known pathogens.
Purpose of the Study:
- To identify and characterize unknown Rhizoctonia solani isolates collected from Texas rice fields.
- To establish the anastomosis group (AG) of the previously designated AG-UNK isolates.
- To document the occurrence and geographic distribution of this Rhizoctonia solani AG in the United States.
Main Methods:
- Isolation of Rhizoctonia solani from soil, sclerotia, stem lesions, and rice residues.
- Anastomosis testing with established tester strains to determine the anastomosis group (AG).
- Morphological characterization (hyphal diameter, nuclei per cell, growth rate, phenol test) and pathogenicity trials on rice and soybean.
Main Results:
- The previously designated R. solani AG-UNK isolates were identified as R. solani AG-11 based on positive anastomosis with AG-11 tester strains.
- Teleomorphs (Thanatephorus cucumeris) were observed on rice sheaths.
- Isolates were pathogenic on foliage in greenhouse trials but caused no significant yield loss in field trials on adult rice plants.
Conclusions:
- This study records the first confirmed occurrence of Rhizoctonia solani AG-11 in Texas.
- The identity of the AG-UNK group is established as AG-11, clarifying previous taxonomic uncertainty.
- The known geographic range of R. solani AG-11 in the United States has been expanded.
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